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Blood Flow-Velocity
 
Velocity of flowing blood, usually measured in cm/s. It is always zero at the vessel wall and the velocity profile across a vessel can have various shapes depending upon the type of flow being observed. Laminar flow giving rise to a laminar velocity profile, plug flow giving rise to a flat velocity profile and disturbed flow can be distinguished.
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• View the DATABASE results for 'Blood Flow-Velocity' (5).Open this link in a new window

Blood Oxygenation Level Dependent ContrastInfoSheet: - Sequences -
Intro, Overview, 
Types of, 
etc.MRI Resource Directory:
 - Functional MRI -
 
(BOLD) In MRI the changes in blood oxygenation level are visible. Oxyhaemoglobin (the principal haemoglobin in arterial blood) has no substantial magnetic properties, but deoxyhaemoglobin (present in the draining veins after the oxygen has been unloaded in the tissues) is strongly paramagnetic. It can thus serve as an intrinsic paramagnetic contrast agent in appropriately performed brain MRI. The concentration and relaxation properties of deoxyhaemoglobin make it a susceptibility , e.g. T2 relaxation effective contrast agent with little effect on T1 relaxation.
During activation of the brain, the oxygen consumption of the local tissue increase by approximately 5% with that the oxygen tension will decrease. As a consequence, after a short period of time vasodilatation occurs, resulting in a local increase of blood volume and flow by 20 - 40%. The incommensurate change in local blood flow and oxygen extraction increases the local oxygen level.
By using T2 weighted gradient echo EPI sequences, which are highly susceptibility sensitive and fast enough to capture the three-dimensional nature of activated brain areas will show an increase in signal intensity as oxyhaemoglobin is diamagnetic and deoxyhaemoglobin is paramagnetic. Other MR pulse sequences, such as spoiled gradient echo pulse sequences are also used.
As the effects are subtle and of the order of 2% in 1.5 T MR imaging, sophisticated methodology, paradigms and data analysis techniques have to be used to consistently demonstrate the effect.
As the BOLD effect is due to the deoxygenated blood in the draining veins, the spatial localization of the region where there is increased blood flow resulting in decreased oxygen extraction is not as precisely defined as the morphological features in MRI. Rather there is a physiological blurring, and is estimated that the linear dimensions of the physiological spatial resolution of the BOLD phenomenon are around 3 mm at best.
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• View the DATABASE results for 'Blood Oxygenation Level Dependent Contrast' (6).Open this link in a new window

 
Further Reading:
  Basics:
IMAGE CONTRAST IN MRI(.pdf)
   by www.assaftal.com    
Vascular Filters of Functional MRI: Spatial Localization Using BOLD and CBV Contrast
  News & More:
A mechanistic computational framework to investigate the hemodynamic fingerprint of the blood oxygenation level-dependent signal
Tuesday, 29 August 2023   by analyticalsciencejournals.onlinelibrary.wiley.com    
The utility of texture analysis of kidney MRI for evaluating renal dysfunction with multiclass classification model
Tuesday, 30 August 2022   by www.nature.com    
MRI Technique Used to Identify Future Risk of Binge Drinking
Monday, 6 January 2020   by www.diagnosticimaging.com    
Gold Acupuncture Needle MRI Pain Discovery
Friday, 3 January 2014   by www.healthcmi.com    
MRI method for measuring MS progression validated
Thursday, 19 December 2013   by www.eurekalert.org    
MRI Resources 
Pediatric and Fetal MRI - Crystallography - Chemistry - Services and Supplies - Brain MRI - Musculoskeletal and Joint MRI
 
Blood Pool AgentsInfoSheet: - Contrast Agents - 
Intro, Overview, 
Characteristics, 
Types of, 
etc.MRI Resource Directory:
 - Contrast Agents -
 
Blood pool agents (intravascular contrast agents) remain in the blood for a prolonged time compared with conventional contrast agents, which diffuse quickly into the interstitial space. Magnetic resonance angiography (MRA), cardiovascular imaging, or contrast enhanced MRIs are possible over an hour or more. This advantage over conventional MRI contrast media allows also higher resolution MRA of several territories using respiratory or cardiac gating techniques with a single contrast bolus.
Different types of blood pool contrast agents:
Blood pool MRI contrast agents with their longer intravascular circulation can be designed to be targeted to necrotic myocardium, to assess myocardial viability, or tumor directed to provide better diagnostic information for various tumors. A disadvantage of the use of blood pool agents for MRA is that the separation of arteries and veins is more difficult because they are present in both and the overlapping of those vessels is disturbing. This can be solved by e.g. different MIP segmentation algorithms.

See also Necrosis Avid Contrast Agent, Tumor Specific Agents, Feruglose, Gadofosveset Trisodium (Vasovist), Ultrasmall Superparamagnetic Iron Oxide and Contrast Medium.
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• View the NEWS results for 'Blood Pool Agents' (1).Open this link in a new window.

• View the DATABASE results for 'Blood Pool Agents' (16).Open this link in a new window

 
Further Reading:
  Basics:
Ablavar Prescribing Information
   by www.ablavar.com    
Lantheus Medical Imaging, Inc. Launches ABLAVAR™ (Gadofosveset Trisodium), a New Diagnostic Magnetic Resonance Angiography Agent
Wednesday, 20 January 2010   by www.radiopharm.com    
Blood-Pool Imaging Using Technetium-99m-Labeled Liposomes(.pdf)
   by jnm.snmjournals.org    
  News & More:
Multimodal Nanoparticles for Quantitative Imaging(.pdf)
Tuesday, 13 December 2011   by alexandria.tue.nl    
MAGNETIC RESONANCE IMAGING OF FOCAL LIVER LESIONS(.pdf)
2002
BlurringInfoSheet: - Artifacts -
Case Studies, 
Reduction Index, 
etc.
 
Blurring comes most obviously from patient motion, but other mechanisms like low resolution sampling also lead to image blurring.
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• View the DATABASE results for 'Blurring' (15).Open this link in a new window

 
Further Reading:
  Basics:
Image Characteristics and Quality
   by www.sprawls.org    
Body CoilForum -
there are related threads
 
The body coil is installed in the magnet and functions both as transmit than also as a receiver coil. This coil has a large measurement field, but does not have the high SNR of special coils. When specific receiver only coils are used (the most surface coils), the body coil serves as the transmit coil.
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• View the NEWS results for 'Body Coil' (1).Open this link in a new window.

• View the DATABASE results for 'Body Coil' (26).Open this link in a new window

 
Further Reading:
  Basics:
System Architecture
2003   by www.revisemri.com    
Magnetic Field
   by hyperphysics.phy-astr.gsu.edu    
  News & More:
Cryogenically-cooled technology significantly enhances current capabilities of cardiac and brain MRI in mice
Wednesday, 14 May 2014   by www.news-medical.net    
MRI Resources 
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